1. Technical Field
This invention relates to an eccentric rolling bearing device for a pumping mechanism employed, for instance, in the anti-skid device of a motor vehicle.
2. Description of the Related Art
The anti-skid device of a motor vehicle operates as follows: When the motor vehicle is braked hard or its is braked while travelling on a slippery road, the device pumps up the hydraulic pressure applied to the wheel cylinders, to prevent brake locking thereby to prevent the slip of the vehicle. The device includes a pumping mechanism for pumping the hydraulic pressure.
FIGS. 2 and 3 show examples of a conventional pumping mechanism. Each of the pumping mechanism converts a rotational motion of a motor 10 into a reciprocating motion of a plunger 11, to perform a pumping action. The plunger 11 is slidably inserted into a cylinder 13 formed in a housing 12.
The pumping mechanism shown in FIG. 2 is designed as follows: An eccentric rolling bearing 16 serving as a cam is mounted on a mounting shaft 15 which is integral with and coaxial with the drive shaft 14 of the motor 10. The bearing 16 comprises an outer race ring 16a and an inner race ring 16b. The outer cylindrical surface of the outer race ring 16 is a cam surface which is in contact with the plunger 11. The inner race ring 16b has an shaft hole at an eccentric position. (cf. Japanese Patent Application (OPI) No. 146220/1990 (the term "OPI" as used herein means an "unexamined published application")
In the conventional pumping mechanism shown in FIG. 3, in which parts corresponding functionally to those which have been described with reference to FIG. 2 are therefore designated by the same reference numerals or characters, a mounting shaft 17 is extended from the drive shaft 14 of the motor 10 in such a manner that it is off-centered (hereinafter referred to as "an eccentric mounting shaft", when applicable), and an ordinary rolling bearing 18 with no inner race ring is mounted on the eccentric shaft 17. In the pumping mechanism, as the eccentric mounting shaft 17 is rotated eccentrically, the rolling bearing 18 is rotated eccentrically as a whole. The outer race ring 18a of the rolling bearing 18 provides a cam surface, with which the plunger 11 is held in slide contact.
In the above-described two conventional pumping mechanisms, the rolling bearings 16 and 18 have the outer race rings 16a and 18a of the rolling bearings 16 and 18 are formed by machining, and they are relatively large in wall thickness. The outer cylindrical surfaces of the outer race rings 16a and 18a are polished. During this polishing operation, a number of stripes 20 are formed in the outer cylindrical surfaces of the outer race rings 16 and 18 in the circumferential direction. Those stripes can be readily observed under a microscope. Hence, the lubricant on the outer cylindrical surface of each of the outer race rings 16 and 18 is divided into a number of parts axially by the stripes; that is, the stripes thus formed make it difficult to form a film of lubricant on the outer cylindrical surface. As a result, the outer cylindrical surface may be seized or worn out where it is in contact with the plunger 11.